Learn French: Qu'un chien errant ait une puce aide à trouver son foyer. - That a stray dog has a microchip helps to find its home.

The clause Qu'un chien errant ait une puce is the subject of the sentence. In French, when a sentence starts with a Que clause acting as the subject, the verb inside that clause must always be in the subjunctive.

What exactly is the subject of the main verb aide?

The entire clause Qu'un chien errant ait une puce acts as a single subject. When a full clause is the subject of a sentence, the main verb is conjugated in the third-person singular, as if the subject were il or cela.

Doesn't une puce usually mean a flea?

Yes, the literal meaning of une puce is a flea! Because of its tiny size, the word is also used for electronic chips and microchips. Context tells us that a microchip, not a flea, helps a stray dog find its home.

Why do we need the preposition à before trouver?

The verb aider requires the preposition à when it is followed by an infinitive verb (meaning to help do something). So, we must say aide à trouver.

Is errant a verb form or an adjective here?